Conventionally, it has been known to provide an off-the-road tire with shoulder lateral grooves connecting between a shoulder main groove and one of tread edges, for example, in order to improve running performance on muddy roads (hereinafter, such performance may be referred to as “mud performance”). In such a tire, the shoulder lateral grooves generate a large shearing force against mud and the mud in the shoulder lateral grooves can be discharged from the one of the tread edges, therefore, a large driving force (traction) is exerted on muddy roads.
By the way, as shown in FIG. 4, a muddy road (a) is formed mainly by a mud layer (b) and a hard soil layer (c) arranged under the mud layer (b), and a surface portion (c1) of the soil layer (c) covered with the mud layer (b) shows a low gripping condition due to high water content. When escaping from the muddy road (a), large grip force is required against the surface portion (c1) of the soil layer, but the conventional tire (t) has not been configured in consideration of exerting such grip force.
Further, if groove volume of the shoulder lateral grooves is increased in order to increase the driving force, vibration of air generated in the shoulder main groove is likely to be discharged from the one of the tread edges, therefore, it is possible that noise performance tends to deteriorate.